1. Field of the Invention
The present invention relates to a system for providing high pressure engine lubricating oil to a variable compression ratio actuator used for the purpose of changing the compression ratio of a reciprocating internal combustion engine.
2. Disclosure Information
Many types of variable compression ratio control systems have been either used in serial production, or at least proposed by designers of automotive reciprocating internal combustion engines. Typically, engines with compression ratio control are operated at lower compression ratio at higher loads and at higher compression ratios at lower and medium loads. In this manner, engine fuel consumption may be minimized. With many types of variable compression ratio (xe2x80x9cVCRxe2x80x9d) systems, it is necessary to provide an external control signal to the VCR mechanism. This presents a dilemma to the engine designer inasmuch as high pressure engine lubricating oil may be provided with an engine driven oil pump, but this is wasteful of energy because under most conditions the higher pressure oil will need to be bypassed or otherwise pressure relieved, and this causes unwanted consumption of energy as well as heating of the oil and possibly foaming when the oil is discharged through a high pressure relief valve system. If, on the other hand, a high pressure source such as an externally mounted hydraulic pump is used for powering a VCR actuator, additional problems arise. More specifically, hydraulic accessories are typically designed to use hydraulic oil as a working fluid. Thus if leakage from the VCR actuator into the interior of the engine occurs, the engine""s lubricating oil would quickly become contaminated with hydraulic fluid. As a result, the need to use hydraulic oil would limit the capability or applicability of VCR actuator control systems.
A system and method according to the present invention solves problems associated with known systems such as that shown in U.S. Pat. No. 2,420,117, in which a single working fluid is used for both the pressurized working fluid and for the fluid being supplied to a VCR actuator. The present system allows high pressure hydraulic fluid to be used as a muscle for providing a supply of high pressure engine lubricating oil to a VCR actuator. The present inventive system allows maximum energy savings because the engine oil pump will be required to furnish only lower pressure oil in the range usually ascribed to such pumps (e.g. pressure less than a 100 PSI), Further, the engine driven accessory hydraulic pump need only have a slight increase in capacity, if any, needed to drive the VCR control system, because the demands imposed by the VCR control system are generally minimal, if nonexistent, at low vehicle speeds such as those encountered in parking lot maneuvering, when the demand upon the accessory hydraulic fluid supply is greatest. And, this is true regardless whether the hydraulic accessory is a power steering gear or an engine radiator cooling fan, because these and other hydraulically powered accessories place the greatest demand on the engine driven accessory hydraulic pump at idle and off-idle operation.
A variable compression ratio control system for an internal combustion engine includes an engine driven accessory hydraulic pump and a hydraulic accumulator system for receiving high pressure hydraulic fluid from the engine driven accessory pump and lower pressure engine oil from an engine oil pump. A variable compression ratio actuator receives high pressure engine lubricating oil from a variable compression ratio supply circuit, which in turn receives high pressure lubricating oil from the hydraulic accumulator system. According to the present invention, the engine driven accessory hydraulic pump may comprise either a power steering pump, or an engine cooling fan pump or other type of pump driven by the engine and providing high pressure hydraulic fluid to various engine accessories. Such pumps may be driven by either a belt, or a chain, or gears, or other drives, as is conventional. The pump may comprise a piston pump, a gear pump, a gerotor pump, or other types of pumps known to those skilled in the art and suggested by this disclosure.
According to another aspect of the present invention, a hydraulic accumulator system for use in a variable compression ratio control system may include a first chamber for receiving hydraulic fluid from an engine driven accessory hydraulic pump, and a second chamber for receiving engine lubricating oil from an engine lubricating oil circuit and for providing highly pressurized lubricating oil to a variable compression ratio supply circuit. Finally, a third chamber is interposed between the first and second chambers and comprises an elastically compressible medium for maintaining pressure within the second chamber as lubricating oil is withdrawn from the second chamber.
According to another aspect of the present invention, a variable compression ratio control system may include as a VCR actuator including a variable length connecting rod such as that disclosed in U.S. patent application Ser. No. 09/682,682 entitled xe2x80x9cVariable Compression Ratio Connecting Rodxe2x80x9d filed on Oct. 5, 2001, which is assigned to the assignee of the present invention and which is hereby incorporated by reference within this specification. Alternatively, a VCR actuator used in a system according to present invention may comprise other types of devices known to those skilled in the art and suggested by this disclosure. What is important here is that the VCR actuator requires a source of high pressure engine lubricating oil furnished by the present system.
According to another aspect of the present invention, a hydraulic accumulator system may include a first gas-charged accumulator having a liquid chamber for receiving hydraulic fluid from an engine driven accessory pump, and a gas chamber communicating with the gas chamber of a second gas-charged accumulator, with the second accumulator having a liquid chamber communicating with the variable compression ratio supply circuit. In this manner, the liquid chamber of the second accumulator supplies high pressure engine lubricating oil to the VCR supply circuit. Alternatively, the hydraulic accumulator system may include a primary accumulator having a first liquid chamber for receiving hydraulic fluid from the engine driven accessory pump and a second liquid chamber communicating with a liquid chamber of a second gas-charged accumulator, as well as with a variable compression ratio supply circuit. In this case, the second liquid chamber of the primary accumulator and the liquid chamber of the secondary gas-charged accumulator will be charged with high pressure engine lubricating oil. With this latter system, the swept volume of the primary and secondary accumulators may be equivalent; alternatively the swept volume of the primary accumulator may be less than the swept volume of the secondary accumulator.
According to another aspect of the present invention, a hydraulic accumulator system according to the present invention may comprise a hydraulic motor driven by hydraulic fluid from an engine driven accessory pump and a control pump coupled to and driven by the hydraulic motor, with the control pump being in fluid communication with and receiving oil flowing from a lubricating oil pump driven by the engine. According to this embodiment a system further includes a gas-charged accumulator having a liquid chamber for receiving pressurized lubricating oil from the control pump, with the liquid chamber of the accumulator being in fluid communication with a variable compression ratio supply circuit. As an alternative, the hydraulic accumulator system may include a hydraulic motor driven by hydraulic fluid from the engine driven accessory pump and a control pump coupled to and driven by the hydraulic motor with the control pump being in fluid communication with oil flowing from a lubricating oil pump driven by the engine. The system further includes a gas-charged accumulator having a liquid chamber for receiving pressurized lubricating oil from the control pump, with the liquid chamber of the accumulator being in fluid communication with the VCR supply circuit and with the power steering system.
According to another aspect of the present invention, a VCR control system for an internal combustion engine includes an engine driven lubricating oil pump and an engine driven accessory hydraulic pump. A hydraulic motor driven by hydraulic fluid from the engine driven accessory pump is coupled to and drive a control pump. The control pump is in fluid communication with oil flowing from the lubricating oil pump. A gas-charged accumulator has a liquid chamber for receiving pressurized lubricating oil from the control pump, with a variable compression ratio supply circuit being in fluid communication with the liquid chamber of the accumulator and with the VCR supply circuit furnishing a high pressure lubricating oil control signal to the variable compression ratio actuator.
According to another aspect of the present invention, a hydraulic motor as described herein may comprise either gear motor or piston motor or another type of motor which converts energy transferred by high pressure hydraulic fluid to circular motion.
According to another aspect of the present invention, a method for powering a variable compression ratio control system of an internal combustion engine includes the steps of providing a source of high pressure hydraulic fluid from an engine driven hydraulic pump, and providing a control pump driven by the high pressure hydraulic fluid. Further, included are the steps of charging a hydraulic accumulator with engine lubricating oil pressurized by the control pump, and feeding high pressure engine lubricating oil to the variable compression ratio actuator. The present method may further comprise a step of providing high pressure hydraulic fluid from the engine driven hydraulic pump to a power steering gear, to a power brake system or to an engine cooling fan or other type of hydraulically powered device.
It is an advantage of the present invention that a system and method according to this invention will provide a variable compression ratio control signal in a form of engine lubricating oil, without causing unnecessary energy consumption arising from avoidable pumping losses.
It is another advantage of the present invention that a system and method according to this invention requires minimum packaging in terms of minimum volume for the underhood portion of the system.
It is another advantage of the present invention that this system and method allow use of VCR actuators driven by engine oil, as opposed to hydraulic fluid. In this method, contamination of the engine lubricating oil by hydraulic fluid is avoided.
It is another advantage of the present invention that this system and method may be used to supply a high pressure lubricating oil control signal to a VCR mechanism which is deep within an engine, such that the lubricating oil will combine with the other lube oil in the engine without the possibility of oil contamination.
Other advantages, as well as features and objects of the present invention will become apparent to the reader of this specification.